This invention generally relates to motor vehicle air bags. More particularly, the invention relates to a driver side air bag module having an integral horn switch which is easily and reliably actuated.
A driver side air bag module is typically mounted upon a motor vehicle's steering wheel. A typical module includes a mounting plate attached to the hub of the steering wheel, an inflator mounted to the mounting plate, an air bag and a cover. The prior art teaches that horn switches can be placed within spokes of the steering wheel. The orientation of this type of horn switch moves relative to the occupant as the steering wheel is rotated. Several other designs have incorporated a horn mechanism into the air bag module cover. The vehicle horn switch was formed by floating the air bag module on a spring assembly within a steering wheel assembly. To actuate the horn the entire module is moved toward the steering wheel hub. This method of horn switch design is expensive and leads to fit and finish problems between the module and the steering wheel.
Another type of horn switch mounts a thin, flexible membrane switch on the back or inner surface of the air bag module cover. Membrane switches conventionally comprise two very thin non-conductive sheets having conductive coatings separated by thin spacers. Pressure on the switch moves the conductive surfaces together to close an electrical circuit and actuate the horn. The membrane switches are expensive and their installation is labor intensive. In the case of a malfunction of the horn switch, the entire air bag module must be replaced as the switch is an integral part of the cover.
The primary object of the invention is to provide an air bag module with a reliable horn switch which is removable without disassembly of the module. Other objects, features, and advantages will become apparent from the following description and appended claims.
Accordingly the invention comprises: a driver side air bag module having an air bag cover, mounting plate, inflator, and cushion. The driver side air bag module cover includes a relatively flexible horn actuation area which is depressible from its front surface by a driver. A substantially airtight pressure chamber is provided inside the air bag module. The chamber may be formed by a thin flexible membrane or bladder. This chamber can be either surrounding or adjacent to the cushion.
A pressure sensitive sensor is mounted either on the interior or exterior surface of the mounting plate and generally behind the horn actuation area. This sensor, which is fluidly coupled to the pressure chamber by means of a passage such as a tube, is responsive to determinable changes in pressure or rates of pressure change within the chamber. The change in pressure is caused by a change in volume of the chamber when the flexible horn actuation area is depressed. The sensor then produces a signal which activates a horn.
In a second embodiment of the invention, the chamber is formed by joining the cover and the mounting plate. A seal, that is sufficiently fluid tight, is provided at the joint between the cover and the mounting plate forming the chamber. Sealing methods between plastic and metal components are known but can include secondary material such as neoprene or other elastomers, or an appropriately designed joint in the plastic cover and base plate. Appropriate sealing is necessary between the inflator and mounting plate.
Further, the sensor can be a differential pressure sensor additionally fluidly coupled to the outside of the module. A differential pressure sensor will measure the change in pressure within the chamber when the horn area is depressed while compensating for changes in atmospheric pressure and temperatures.
It is known that an air bag module cover can be integrally formed into a steering wheel assembly. The module components, including the cushion and inflator, are inserted into the steering wheel. The mounting plate is then attached to the steering wheel with cover to form a steering assembly. The airtight chamber can be formed from the integral steering wheel cover and the mounting plate.
The invention includes a method for producing an air bag module assembly, as well as a method of repairing the air bag module.